This collection contains correspondence, research notes, papers and addresses, memoranda, drafts of letters and papers. These items center on Lingelbach's career at the University of Pennsylvania and at the American Philosophical Society. There is much correspondence with noted historians relating to various topics. His interest in political history and foreign policy, and his participation in national organizations can be seen in such files as the Foreign Policy Association, National Resources Planning Board, and the U.S. War Dept. Committee on Education and Special Training (World War I).